The present invention relates to a lubricating composition containing a lubricating oil, particularly to a lubricating composition used as being charged or being charged and coated on metal substrates in various forms, and a sliding member composed of the lubricating composition.
A sliding member in which a sliding surface of a metal substrate is charged and coated with a lubricating composition has been conventionally and widely used for various mechanical parts.
As an example, it is explained so-called solid lubricant-embedding sliding members in which apertures or grooves are formed to a metal substrate made of copper alloys or iron alloys and a solid lubricant is embedded and fixed in such apertures or grooves, have been used for various kinds of machine parts.
As a manufacturing method for the solid lubricant-embedding sliding member includes, a method (1) of using a round graphite rod having spiral ridges formed at the outer circumferential surface as a core in a casting mold, casting a molten metal into the casting mold, and removing the core by the cutting, thereby exposing the solid lubricant (graphite) spirally to the sliding surface (Japanese Patent Publication No 39-2506 (1964)); a method (2) of adhering and fixing solid lubricant pellets (cylindrical form) to paper or film which is burnt to be eliminated upon casting of a molten metal adhering and fixing the obtained solid lubricant pellets to the outer circumferential surface of a core rod composed of a shell sand mold to form a core in the casting mold (Japanese Patent Publication No 56-14381(1981)), or adhering and fixing solid lubricant pellets to a core rod composed of a shell sand mold to form a core for the casting mold (Japanese Patent Publication No 52-5449(1977)), casting a molten metal into the casting mold, thereby exposing the solid lubricant pellets on the sliding surface; or a method (3) of forming apertures or grooves to a metal substrate and embedding and fixing solid lubricant pellets coated with adhesives into the apertures or grooves, may be cited.
In the manufacturing methods described above, the method (1) has drawbacks that the molten metal can not extend sufficiently upon casting since graphite of good heat conductivity is used as it is for the core and the shape of the sliding member is restricted, and the method (2) has drawbacks that the solid lubricant pellets are detached or displaced during casting and it is difficult to obtain a sliding member in which the solid lubricant pellet are arranged regularly. Accordingly, the method (3) described in the above has been used generally.
However, the method (3) also involves several technical problems.
(a) Since the size of the apertures (aperture diameter) disposed in the metal substrate is different depending on the size of the metal substrates, the solid lubricant pellets embedded into such apertures having various sizes have to be prepared corresponding to the varying aperture thereof.
(b) Since it is difficult to automate the operation of embedding the solid lubricant pellets coated with adhesives and it has to be down manually, the workability is extremely poor.
(c) Since the solid lubricant pellets can not be used for embedding and fixing solid lubricant into grooves, for example, spiral grooves or ring-shaped grooves disposed in the inner surface of a metal substrate, in particular, a cylindrical metal substrate, it is necessary to provide a paste-like solid lubricant having a fluidity.
Further, as an additional problem, skin eruption or like of other unexpected accident may occur to operators during coating operation of adhesives to the solid lubricants in view of the item (b) described above.
Further, the following solid lubricant have been known:
A lubricant containing heat-molded composition comprising a polymeric synthetic resinous base material blended with a lubricant adsorbent carrier, the carrier having a lubricant adsorbed thereon, and molded, the carrier having a melting point or a melt viscosity higher than the base material, having a surface area of at least 0.01 m.sup.2 /g, and being selected from the group consisting of
(1) a non-fusible inorganic material; PA1 (2) a synthetic high molecular weight polymeric resinous material; PA1 (3) a naturally occurring high molecular weight polymeric material; and PA1 (4) mixtures thereof; and
the base material being selected from the group consisting of a polymeric synthetic resin and a mixture of at least two polymeric synthetic resins (U.S. Pat. No. 3,778,918);
A sliding surface embedding-type solid lubricant comprising a solid lubricant powder, a thermosetting synthetic resin or an ordinary temperature setting-type synthetic resin which is liquid under an ordinary temperature for bonding the powdery particles and a lubricating oil impregnated between each of the powdery particles bonded by the synthetic resin (Japanese Patent Application Laid-Open (KOKAI) No. 58-160398(1983));
A composite lubricating material which can be molded into a desired shape and have a high surface strength, comprising 0.5 to 90.0% by weight of a pulverized, surface-treated and expanded graphite product (a+b) obtained by subjecting from 5 to 99.5% by weight of an expanded graphite powder (a) having an apparent specific gravity of 0.01 to 0.50 obtained by wet oxidation of natural graphite, kish graphite and artificial graphite, and then expanding and disintegrating them under a high temperature heat treatment, to surface treatment with 0.5 to 95.0% by weight of a lubricating oil (b) , for example, turbine oil, machine oil, spindle oil and bearing oil, and 10 to 99.5% by weight of an organic binder (c) composed of a thermosetting synthetic resin such as phenol resin, melamine resin, epoxy resin and polyimide resin, or a thermoplastic synthetic resin such as polyphenylene sulfide, polyacetal, polytetrafluoroethylene, nylon 6, nylon 11 and polyurethane (Japanese Patent Application Laid-Open (KOKAI) No. 63-23993 (1988));
An extrudable or injection moldable self-lubricating composition comprising 100 parts by weight of a molding product composed of 99 to 10 parts by weight of a lubricating oil and 20 to 90 parts by weight of a super high molecular weight-polyethylene, and 0.1 to 20 parts by weight of a powder blended therewith (Japanese Patent Application Laid-Open (KOKAI) No. 63-161075 (1988)); and
A composite bearing material comprising 0.1 to 10% by weight of fiber material having a good affinity for oil, 1 to 15% by weight of lubricating oil and the remainder of synthetic resin, with which pores and surfaces of a porous metallic layer provided on a metallic backing are impregnated and coated (U.S. Pat. No. 4,308,153).
The composite bearing material disclosed in the U.S. Patent '153 may contain 0.1 to 10% by weight of a solid lubricant such as graphite and 0.1 to 10% by weight of a metallic soap. The U.S. Patent '153 also discloses a thermoplastic resin as the synthetic resin and the actually used synthetic resin was polyacetal.
On the other hand, under the consideration of the performance of the sliding member, since the embedded solid lubricant is supplied little by little to the sliding surface to form a solid lubricant film, it can be served for the long time use without additionally supplying the lubricant. However, since the application use is substantially restricted to that in a low speed and high load region, the combined use with a lubricating oil is inevitable in an application use as being out of the above-mentioned region. In addition, the lubricant containing thermoplastic resin as disclosed in the patent '153 generally has low bonding strength to a metal substrate, resulting in detaching of the lubricant.
Accordingly, in the solid lubricant-embedding sliding member to be used in the application use out of the above-mentioned region, it is required to form grooves to the sliding surface as grease pits or to supply the lubricating oil from the oil feeding device to the sliding surface.
For the foregoing problems in view of manufacture and performance, the present inventors have considered that the all of the problems described above can be overcome thoroughly by satisfying all of the technical subjects, namely, (1) the lubricating composition can be embedded without restrictions at all, to the size and the shape of the apertures or grooves disposed in the metal substrate, (2) the solid lubricant embedded can provide both of the lubricating effect by the lubricating oil and the lubricating effect by the solid lubricant powder material and (3) the solid lubricant can be bonded to the apertures or grooves in the metal substrate, and as a result of an earnest study, it has been found that by blending a solid lubricant powder material with a lubricating oil which is in a liquid or paste-like form under an ordinary temperature, a carrier for absorbing and possessing the lubricating oil, and a thermosetting synthetic resin binder, the thus-obtained lubricating composition has a wettability and a fluidity, and the solid lubricant obtained therefrom is bonded to the apertures or grooves disposed in the metal substrate even if it contains the lubricating oil. On the basis of the finding, the present invention has been attained.